An ultrasound imaging system includes a transducer array that transmits an ultrasound beam into an examination field of view. As the beam traverses structure (e.g., of a sub-portion of an object or subject) in the field of view, sub-portions of the beam are attenuated, scattered, and/or reflected off the structure, with some of the reflections (echoes) traversing back towards the transducer array. The transducer array receives echoes, which are processed to generate an image of the sub-portion of the object or subject. The image is visually displayed.
Ultrasound imaging is used in a wide range of medical and non-medical applications. An example of a medical application is ultrasound guided biopsy. Generally, a biopsy is a procedure in which a small sample(s) of tissue of interest (e.g., prostate, lung, breast, etc.) is removed for subsequent examination for abnormalities such as cancer cells. For a biopsy, a needle is inserted through the skin and advanced to the target tissue where the sample(s) is taken. A biopsy typically is performed in response to finding a lump, abnormal physical enlargement of tissue, etc.
With ultrasound guided biopsy, ultrasound is used to assist a clinician with locating and/or navigating the needle to the tissue of interest. A non-limiting approach is described in Pelissier et al., Ser. No. 12/775,403, filed May 6, 2010, and entitled “Freehand Ultrasound Imaging Systems and Method for Guiding Find Elongate Instruments,” which is incorporated herein by reference in its entirety. In '403, electro-magnetic sensors are affixed to both the ultrasound probe and a needle instrument, and communicate with a position tracking system, which monitors the position and orientation thereof.
In '403, the transducer probe is placed against the patient and 2D data is acquired. The location of the probe (and the needle where the needle instrument is affixed to the probe), relative to the ultrasound image, is determined from the tracking sensors on the probe. In '403, where the needle instrument is not affixed to the probe, once the target tissue is located, the location of the needle, relative to the ultrasound image, is determined from the tracking sensors on the needle instrument. Both scenarios allow the clinician to determine the location of the probe and/or the needle in 3D space.
With another approach, structural 3D volumetric image data from a second modality is also used for guidance. MRI systems, generally, are capable of capturing high resolution, 3D data that is rich in internal structure and features. Ultrasound, in comparison, is capable of capturing low to medium-high resolution data sets, both two-dimensional and three-dimensional, at high acquisition rates that can support real-time interaction. For this approach, the 3D MRI image data is acquired before the biopsy. Then, during the biopsy, the 2D ultrasound data is fused with the 3D MRI data.
This has included segmentation to delineate different tissue types followed by registration of the 2D US data and the 3D MRI data. The scale and structure of the data sets produced by these two modalities is generally very different due to the different physical information captured by the modalities, requiring an initial “normalization” procedure to remap one or both of the data sets to bring them as closely as possible into structurally comparable spaces. The fused data and the tracking system are used to guide the probe to the target tissue, which is identified from the structural image data.
Unfortunately, electro-mechanical sensor based tracking systems often require expensive equipment and manual procedures in order to extract critical information concerning the presence and extent of malignancies. Even the latest ultrasound and MRI fusion-based systems require expensive hardware-based tracking technology. Furthermore, currently, the clinician will take more samples than is absolutely necessary, in both target tissues and surrounding tissue due to uncertainty in both correlation and tracking. This may lead to increased procedure time and patient discomfort.